1. Field of the Invention
The present invention relates to a zoom lens adapted for use in a compact camera such as a camera with lens shutter.
2. Related Background Art
Compact cameras with lens shutter have been more and more automated in recent years, with various functions such as automatic focusing, automatic film loading, date recording, incorporated electronic flash etc. as standard equipment, and have become accepted by wider and wider users. Recently there are also commercialized those with a lens of multiple focal lengths, for expanding the field of application further.
Zoom lens of simplest structure suitable for such compact cameras is a two-group telescopic zoom lens composed of a first lens group G.sub.1 of a positive refractive power and a second lens group G.sub.2 of a negative refractive power. In comparison with the usual lenses for single lens reflex cameras, such lens is more suitable for the cameras with lens shutter, having less restriction on the behind-lens focal length and can achieve compactization by reducing said behind-lens focal length to a certain extent.
However the zoom lenses of this kind proposed before are mostly with focal length in a range of f =40-60 mm and F-number in a range of 4-5.6, and, even in bright lenses with high zooming ratios, the focal length and the F-number are still in ranges of f=35-70 mm and F=3.5-6.7.
Among such lenses, some are designed with an extremely short behind-lens focal length in order to reduce the entire length of the lens. Consequently, even if compactization is achieved in this manner, there may result internal reflections between the last lens face of the lens system and the film plane, eventually leading to the formation of ghost image deteriorating the image quality. Besides the second lens group G.sub.2 positioned close to the film plane becomes inevitably large as the diameter thereof has to be close to the size of the film.
Also in such zoom lenses, since the refractive powers of the lens groups are relatively limited in order to secure the imaging performance, there is required a large moving amount for the lens groups for a given zoom ratio, leading to a large lens system.